Since Bookeen published their dual firmware (forcing us to choose between mobi and epub), I've been torn. I've bought many books in mobipocket format, it looks like a huge inconvinience to update my device to ePub and loose all those books (or having to convert them, but most have DRM).
I guess we have to clean the slate sometime to start something good from the ground up. Maybe when I buy a second ereader that won't be an issue.